1. Field of the Invention
This invention relates to the field of disk drive storage devices. More particularly, this invention relates to the field of forming a gimbal dimple for supporting a read/write head on the end of a disk drive suspension.
2. Description of Related Art
A disk drive generally uses a spinning storage medium (e.g. a disk) to store data. A read/write head is positioned in close proximity to the disk by a suspension assembly. In a hard disk drive, a suspension assembly commonly refers to the combination of a slider/head, containing the read-write transducer circuitry affixed to the distal end of the suspension. The suspension supports the read/write head by a gimbaling means so that the read/write head can pitch and roll. Pitch and roll are required to compensate for disk surface imperfections and aerodynamic forces caused by the wind of a rapidly spinning disk. One such gimbaling means is through a flexible piece of metal, a flexure, perched on top of gimbal dimple.
A head suspension generally comprises a load beam and a flexure. The flexure is located at the distal end of the load beam, which overhangs a disk. A flexure may be a separate part which is welded to a load beam or may be integrally formed in the load beam. Commonly, the part of the flexure which is perched on top of a gimbal dimple is an inwardly cantilevered pad, or tongue. The flexure is otherwise mounted rigidly to the load beam.
The gimbal dimple, sometimes referred to as a load point dimple or dimple, may be formed from the material of the flexure or the material of the load beam. Either material may be referred to as a dimple substrate or substrate. In operation, the protruding surface of the dimple abuts a flat engagement surface of the opposing part. For example, if the gimbal dimple is formed from the material of the load beam, then the opposing part is the flexure tongue. If the gimbal dimple is formed from the material of the flexure, then the opposing part is the load portion of the load beam. The flat engagement surface of the opposing part is designed to rock and sway around the dimple surface yet stay abutted to it. The means of measuring the contact force of this abutment is described in published application US2005/0005425, filed May 17, 2004, and entitled “Method and apparatus for HDD suspension gimbal-dimple separation (contact) force measurement,” now abandoned. To promote even gimbaling, the surface around the apex of the dimple is sometimes spherically radiused.
A gimbal dimple can be formed by masking and partially etching the surface of the substrate, or it can be formed by plastically deforming the substrate using a dimple punch and die. The remainder of this discussion will pertain to a punched dimple.
A punched dimple has a protruding side or surface, which is generally convex. The protruding surface can be referred to as the outer surface. A punched dimple, unlike an etched dimple, has a recessed side or surface on the opposite side from the protruding surface. The recessed side is generally concave. The recessed surface can be referred to as the inner surface.
As stated, a gimbal dimple can be formed using a dimple punch and die. Both a dimple punch and a die are typically precision machined tools which are part of a larger fabrication machine. The two tools typically act in concert with a pressure pad or plate which holds a workpiece, such as a gimbal substrate, in place. A workpiece can include any plastically deformable material, such as stainless steel.
A dimple punch, sometimes simply called a punch, is typically an elongated, hardened steel with a rounded tip at one end. The rounded tip may have a precise spherical radius, or it may take the form of other rounded shapes. Typically, the rounded tip of the tool smoothly transitions into a conical tapered body. The surfaces of the tip and tapered body are commonly the work surfaces which contact the workpiece.
A die is sometimes referred to as a form die, gimbal form die, female form die, or dimple form stripper insert. A dimple form die is typically a hardened steel tool with a hole in its otherwise flat work surface. To form a dimple in a workpiece, the workpiece is clamped over the hole in the die using a pressure pad or plate. The dimple punch is then punched into the workpiece directly over the die hole. The recessed surface of the dimple is formed on the side in which the dimple punch is punched, and the protruding surface is formed in the die hole.
The hole in the die can be a through hole or a blind hole. A through hole, or thru hole, is a hole through the entire depth of the die. A through hole may also refer to a hole through a substantial portion of the die, such that the apex of the outside surface of a dimple will not touch the bottom of the hole during the punching process. In contrast, a blind hole is a relatively shallow hole, such that the apex of the outside surface of a dimple will touch the bottom of the hole during the punching process. Either type of hole may be generally cylindrical, having been drilled from the die body, or shaped in other ways by precision machining. Dies with through holes or blind holes can be referred to as through hole dies or blind dimple dies, respectively.
One problem encountered in the prior art is that the gradual transition of a dimple from the plane of the substrate where it is formed makes rounded dimples difficult for optical systems to precisely locate. Optical and vision systems are known to be used to mount and align head sliders to flexures, and it is critical to such systems that they can precisely locate gimbal dimples in order to ensure proper location and alignment of the head slider. The rounded shape of current dimples does not always create a sharply defined profile that is easily sensed by an optical system.
A partial solution to this problem is to use a blind dimple die when punching a gimbal dimple. Blind dimple dies tend to produce shinier, more reflective dimples, which are easier for optical systems to see. However, there are drawbacks to using blind dimple dies. A blind dimple die is more difficult to fabricate than a through hole die. A blind hole has a precise 3-dimensional contour, such as a spherical radius, on its bottom. A 3-dimensional contoured bottom requires time and labor to fabricate and quality check. In contrast, a through hole has no bottom. Also, a blind dimple die is more difficult to resurface than a through hole die. If the top surface of a blind dimple die is ground down for resurfacing, then its blind hole must be deepened by an equivalent amount. Again, a through hole has no bottom. Thus, a blind dimple die is not necessarily an optimal solution in comparison with a through hole die.
Another problem with the prior art is that punching a substrate often has the side effect of distorting the otherwise flat substrate surrounding the punched area. Thus, the periphery around a punched dimple along with the area outside the periphery can have distortions. The varying rate of planar change can affect the height of a lift tab at the end of a load beam and increases component variability. It is preferable to minimize such variability.
There is a need for an improved gimbal dimple in a head suspension and an improved method for making such a dimple. Specifically, there is a need for a dimple which is easier for optical systems to locate. Preferably, such a dimple would be formed using a through hole die but have the increased reflectivity of a dimple formed using a blind dimple die.
Also, there is a need for a punched gimbal dimple whose periphery and area outside the periphery is flatter than those of the prior art.